Type physicalism (also known as
reductive materialism,
type identity theory,
mind-brain identity theory and
identity theory of mind) is a theory, in
philosophy of mindPhilosophy of mind is a branch of modern analytic philosophy that studies the nature of the mind, mental events, mental functions, mental properties, consciousness and their relationship to the physical body, particularly the brain. The mind-body problem, i.e...
, which asserts that
mental eventA mental event is a particular occurrence of something going on in the mind or mind substitute. It can be a thought, a dream, a feeling, a realization, or any other mental activity. Mental events are not limited to human thought but can be associated with animal and artificial intelligence as...
s are type-identical to the physical events in the brain with which they are
correlatedIn statistics, correlation indicates the strength and direction of a relationship between two random variables. The commonest use refers to a linear relationship. In general statistical usage, correlation or co-relation refers to the departure of two random variables from independence...
. The thesis of type
physicalismPhysicalism is a philosophical position holding that everything which exists is no more extensive than its physical properties; that is, that there are no kinds of things other than physical things...
is that mental event types (for example, pains) are identical, perhaps contingently, with specific physical event types in the brain (for example, C-fiber firings).
It is called
type identity in order to distinguish it from a similar but distinct theory called the
token identityAnomalous monism is a philosophical thesis about the mind-body relationship. It was first proposed by Donald Davidson in his 1970 paper Mental events. The theory is twofold and states that mental events are identical with physical events, and that the mental is anomalous, i.e. under their mental...
theory. The
type-token distinctionIn philosophy and knowledge representation, the type-token distinction is a distinction that separates an abstract concept from the objects which are particular instances of the concept...
is easily illustrated by way of example. In the phrase "yellow is yellow is yellow is yellow", there are only two types of words ("yellow" and "is") but there are seven tokens (four "yellow" and three "is" tokens).
Background
According to
U.T. PlaceUllin Place was a British philosopher and psychologist. Along with J. J. C. Smart, he developed the identity theory of mind. Place was born in Yorkshire and studied under Gilbert Ryle at Oxford University. There, he became acquainted with philosophy of mind in the logical behaviorist tradition,...
, one of the popularizers of the idea of type-identity in the 1950s and 1960s, the idea of type-identity physicalism originated in the 1930s with the psychologist E. G. Boring and took nearly a quarter of a century to gain acceptance from the philosophical community. Boring, in a book entitled
The Physical Dimensions of Consciousness (1933) wrote that:
To the author a perfect correlation is identity. Two events that always occur together at the same time in the same place, without any temporal or spatial differentiation at all, are not two events but the same event. The mind-body correlations as formulated at present, do not admit of spatial correlation, so they reduce to matters of simple correlation in time. The need for identification is no less urgent in this case (p. 16, quoted in Place [unpublished]).
The barrier to the acceptance of any such vision of the mind, according to Place, was that philosophers and logicians had not yet taken a substantial interest in questions of identity and referential identification in general. The dominant
epistemologyEpistemology or theory of knowledge is the branch of philosophy concerned with the nature and scope of knowledge...
of the
logical positivistsLogical positivism is a school of philosophy that combines empiricism, the idea that observational evidence is indispensable for knowledge of the world, with a version of rationalism incorporating mathematical and logico-linguistic constructs and deductions in epistemology.[See, e.g., : ...]
at that time was
phenomenalismIn epistemology and the philosophy of perception, phenomenalism is the view that physical objects do not exist as things in themselves but only as perceptual phenomena or sensory stimuli situated in time and in space...
, in the guise of the theory of sense-data. Indeed Boring himself subscribed to the phenomenalist creed, attempting to reconcile it with an identity theory and this resulted in a
reductio ad absurdum of the identity theory, since brain states would have turned out, on this analysis, to be identical to colors, shapes, tones and other sensory experiences.
The revival of interest in the work of
Gottlob FregeFriedrich Ludwig Gottlob Frege was a German mathematician who became a logician and philosopher. He was one of the founders of modern logic, and made major contributions to the foundations of mathematics. As a philosopher, he is generally considered to be the father of analytic philosophy, for his...
and his ideas of
senseSenses are the physiological methods of perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology , and philosophy of perception...
and
referenceA reference, or a references point, is the intensional use of one thing, a point of reference or reference state, to indicate something else...
on the part of
Herbert FeiglHerbert Feigl was an Austrian philosopher and a member of the Vienna Circle.The son of a weaver, Feigl was born in Reichenberg , Bohemia, and matriculated at the University of Vienna in 1922...
and J.J.C. Smart, along with the discrediting of phenomenalism through the influence of the later
WittgensteinLudwig Josef Johann Wittgenstein was an Austrian-British philosopher who worked primarily in logic, the philosophy of mathematics, the philosophy of mind, and the philosophy of language....
and J.L. Austin, led to a more tolerant climate toward physicalistic and realist ideas.
Logical behaviorismBehaviorism , also called the learning perspective , is a philosophy of psychology based on the proposition that all things which organisms do — including acting, thinking and feeling — can and should be regarded as behaviors...
emerged as a serious contender to take the place of the Cartesian "ghost in the machine" and, although not lasting very long as a dominant position on the mind/body problem, its elimination of the whole realm of internal mental events was strongly influential in the formation and acceptance of the thesis of type identity.
Versions of type identity theory
There were actually subtle but interesting differences between the three most widely credited formulations of the type-identity thesis, those of Place, Feigl and Smart which were published in several articles in the late 1950s. However, all of the versions share the central idea that the mind is identical to something physical.
U.T. Place
U.T. Place's (1956) notion of the relation of identity was derived from
Bertrand RussellBertrand Arthur William Russell, 3rd Earl Russell, OM, FRS was an English philosopher, logician, mathematician, historian, and social critic. Although he spent the majority of his life in England, he was born in Wales, where he also died.Russell led the British "revolt against idealism" in the...
's distinction among several types of
is statements: the
is of
identityIn philosophy, identity is whatever makes an entity definable and recognizable, in terms of possessing a set of qualities or characteristics that distinguish it from entities of a different type...
, the
is of equality and the
is of composition. Place's version of the relation of identity is more accurately described as a relation of composition. For Place, higher-level mental events are composed out of lower-level physical events and will eventually be analytically reduced to these. So, to the objection that "sensations" do not mean the same thing as "mental processes", Place could simply reply with the example that "lightning" does not mean the same thing as "electrical discharge" since we determine that something is lightning by looking and seeing it, whereas we determine that something is an electrical discharge through experimentation and testing. Nevertheless, "lightning is an electrical discharge" is true since the one is composed of the other.
Feigl and Smart
For
FeiglHerbert Feigl was an Austrian philosopher and a member of the Vienna Circle.The son of a weaver, Feigl was born in Reichenberg , Bohemia, and matriculated at the University of Vienna in 1922...
(1957) and
SmartJohn Jamieson Carswell "Jack" Smart AC , often referred to as J.J.C. Smart, is an Australian emeritus professor of philosophy at Monash University, Australia...
(1959), on the other hand, the identity was to be interpreted as the identity between the referents of two descriptions (senses) which referred to the same thing, as in "the morning star" and "the evening star" both referring to Venus. So to the objection about the lack of equality of meaning between "sensation" and "brain process", their response was to invoke this Fregean distinction: "sensations" and "brain" processes do indeed
mean different things but they refer to the same physical phenomenon. Moreover, "sensations are brain processes" is a contingent, not a necessary, identity.
Multiple realizability
One of the most influential and common objections to the type identity theory is the argument from
multiple realizabilityMultiple realizability, in philosophy of mind, is the thesis that the same mental property, state, or event can be implemented by different physical properties, states or events...
. The multiple realizability thesis asserts that mental states can be realized in multiple kinds of systems, not just brains, for example. Since the identity theory identifies mental events with certain brain states, it does not allow for mental states to be realized in organisms or computational systems that do not have a brain. This is in effect an argument that the identity theory is too narrow because it does not allow for organisms without brains to have mental states. However,
token identity (where only particular tokens of mental states are identical with particular tokens of physical events) and
functionalismFunctionalism is a theory of the mind in contemporary philosophy, developed largely as an alternative to both the identity theory of mind and behaviourism. Its core idea is that mental states are constituted solely by their functional role — that is, they are causal relations to other mental...
both account for multiple realizability.
The response of type identity theorists, such as Smart, to this objection is that, while it may be true that mental events are multiply realizable, this does not demonstrate the falsity of type identity. As Smart states:
- "The functionalist second order [causal] state is a state of having some first order state or other which causes or is caused by the behavior to which the functionalist alludes. In this way we have a second order type theory."
The fundamental point is that it is extremely difficult to determine where, on the continuum of first order processes, type identity ends and merely token identities begin. Take Quine's example of English country gardens. In such gardens, the tops of hedges are cut into various shapes, for example the shape of an elf. We can make generalizations over the type
elf-shaped hedge only if we abstract away from the concrete details of the individual twigs and branches of each hedge. So, whether we say that two things are of the same type or are tokens of the same type because of subtle differences is just a matter of descriptive abstraction. The type-token distinction is not all or nothing.
Hilary PutnamHilary Whitehall Putnam is an American philosopher who has been a central figure in analytic philosophy since the 1960s, especially in philosophy of mind, philosophy of language, and philosophy of science...
responds to Smart's response by essentially rejecting functionalism because, he believes, it is indeed a second-order type identity theory. Putnam uses multiple realizability against functionalism itself, suggesting that mental events (or kinds, in Putnam's terminology) may be diversely implemented by diverse functional/computational kinds; there may be only a token identification between particular mental kinds and particular functional kinds. Putnam, and many others who have followed him, now tend to identify themselves as generically non-reductive physicalists. Putnam's invocation of multiple realizability does not, of course, directly answer the problem raised by Smart with respect to useful generalizations over types and the flexible nature of the type-token distinction in relation to causal taxonomies in science.
Qualia
Another frequent objection is that type identity theories fail to account for phenomenal mental states (or
qualia"Qualia" , singular "quale" , from the Latin for "what sort" or "what kind," is a term used in philosophy to describe the subjective quality of conscious experience. Examples of qualia are the pain of a headache, the taste of wine, or the redness of an evening sky...
), such as having a pain, feeling sad, experiencing nausea. (Qualia are merely the subjective qualities of
conscious experienceConsciousness is subjective experience or awareness or wakefulness or the executive control system of the mind. It is an umbrella term that may refer to a variety of mental phenomena...
. An example is the way the pain of jarring your elbow
feels to you.) Arguments can be found in Saul Kripke (1972) and David Chalmers (1996), for example, according to which the identity theorist cannot identify phenomenal mental states with brain states (or any other physical state for that matter) because one has a sort of direct awareness of the nature of such qualitative mental states, and their nature is qualitative in a way that brain states are not.
A famous formulation of the qualia objection comes from
Frank JacksonFrank Cameron Jackson is an Australian philosopher, currently Distinguished Professor and former Director of the Research School of Social Sciences at Australian National University. In 2007-2008, he will also become a regular visiting professor of philosophy at Princeton University...
(1982) in the form of the
Mary's roomMary's room is a philosophical thought experiment proposed by Frank Jackson in his article "Epiphenomenal Qualia" and extended in "What Mary Didn't Know"...
thought experiment. Let us suppose, Jackson suggests, that a particularly brilliant super-scientist named Mary has been locked away in a completely black-and-white room her entire life. Over the years in her colour-deprived world she has studied (via black-and-white books and television) the sciences of neurophysiology, vision and electromagnetics to their fullest extent; eventually Mary comes to know all the physical facts there are to know about experiencing colour. When Mary is released from her room and experiences colour for the first time, does she learn something new? If we answer "yes" (as Jackson suggests we do) to this question, then we have supposedly denied the truth of type physicalism, for if Mary has exhausted all the physical facts about experiencing colour prior to her release, then her subsequently acquiring some new piece of information about colour upon experiencing its quale reveals that there must be something about the experience of colour which is not captured by the physicalist picture. (See
Mary's roomMary's room is a philosophical thought experiment proposed by Frank Jackson in his article "Epiphenomenal Qualia" and extended in "What Mary Didn't Know"...
page for full discussion).
The type identity theorist, such as Smart, attempts to explain away such phenomena by insisting that the experiential properties of mental events are
topic-neutral. The concept of topic-neutral terms and expressions goes back to
Gilbert RyleGilbert Ryle , was a British philosopher, and a representative of the generation of British ordinary language philosophers influenced by Wittgenstein's insights into language, and is principally known for his critique of Cartesian dualism, for which he coined the phrase "the ghost in the machine"...
, who identified such topic-neutral terms as "if", "or", "not", "because" and "and." If one were to hear these terms alone in the course of a conversation, it would be impossible to tell whether the topic under discussion concerned geology, physics, history, gardening or selling pizza. For the identity theorist, sense-data and qualia are not real things in the brain (or the physical world in general) but are more like "the average electrician." The average electrician can be further analyzed and explained in terms of real electricians but is not itself a real electrician.
See also
- Consciousness
Consciousness is subjective experience or awareness or wakefulness or the executive control system of the mind. It is an umbrella term that may refer to a variety of mental phenomena...
- Eliminative materialism
Eliminative materialism is a materialist position in the philosophy of mind. Its primary claim is that people's common-sense understanding of the mind is false and that certain classes of mental states that most people believe in do not exist...
- Emergent materialism
In the philosophy of mind, emergent materialism is a theory which asserts that the mind is an irreducible existent in some sense, albeit not in the sense of being an ontological simple, and that the study of mental phenomena is independent of other sciences.The view can be divided into emergence...
- Materialism
The philosophy of materialism holds that the only thing that exists is matter; that all things are composed of material and all phenomena are the result of material interactions. In other words, matter is the only substance. As a theory, materialism is a form of physicalism and belongs to the...
- Mind-body problem
- Monism
Monism is any philosophical view which holds that there is unity in a given field of inquiry, where this is not to be expected. Thus, some philosophers may hold that the Universe is really just one thing, despite its many appearances and diversities; or theology may support the view that there is...
- Philosophy of mind
Philosophy of mind is a branch of modern analytic philosophy that studies the nature of the mind, mental events, mental functions, mental properties, consciousness and their relationship to the physical body, particularly the brain. The mind-body problem, i.e...
- Physicalism
Physicalism is a philosophical position holding that everything which exists is no more extensive than its physical properties; that is, that there are no kinds of things other than physical things...
- Presentism
In the philosophy of time, presentism is the theory that only present things exist, and future and past things are unreal. Past and future "entities" are to be construed as logical constructions or fictions. The opposite of presentism is 'eternalism', which is the belief that things in the past and...
External links